Phylogeography of the sergeantsAbudefduf sexfasciatusandA. vaigiensisreveals complex introgression patterns between two widespread and sympatric Indo‐West Pacific reef fishes

Abstract

On evolutionary timescales, sea level oscillations lead to recurrent spatio-temporal variation in species distribution and population connectivity. In this situation, applying classical concepts of biogeography is challenging yet necessary to understand the mechanisms underlying biodiversity in highly diverse marine ecosystems such as coral reefs. We aimed at studying the outcomes of such complex biogeographic dynamics on reproductive isolation by sampling populations across a wide spatial range of a species-rich fish genus: the sergeants (Pomacentridae: Abudefduf). We generated a mutlilocus data set that included ten morpho-species from 32 Indo-West Pacific localities. We observed a pattern of mito-nuclear discordance in two common and widely distributed species: Abudefduf sexfasciatus and Abudefduf vaigiensis. The results showed three regional sublineages (Indian Ocean, Coral Triangle region, western Pacific) in A. sexfasciatus (0.6-1.5% divergence at cytb). The other species, A. vaigiensis, is polyphyletic and consists of three distinct genetic lineages (A, B and C) (9% divergence at cytb) whose geographic ranges overlap. Although A. vaigiensis A and A. sexfasciatus were found to be distinct based on nuclear information, A. vaigiensis A was found to be nested within A. sexfasciatus in the mitochondrial gene tree. A. sexfasciatus from the Coral Triangle region and A. vaigiensis A were not differentiated from each other at the mitochondrial locus. We then used coalescent-based simulation to characterize a spatially widespread but weak gene flow between the two species. We showed that these fishes are good candidates to investigate the evolutionary complexity of the discrepancies between phenotypic and genetic similarity in closely related species.

The Indo-Pacific Sergeant Abudefduf vaigiensis (Quoy & Gaimard, 1825) (Perciformes: Pomacentridae) in Libya, South-Central Mediterranean Sea

“…Molecular results obtained here are in agreement with data reported by Bertrand et al [27], who noticed that an A. vaigiensis lineage was found to be nested within A. sexfasciatus in the mitochondrial gene tree, whereas both species were only found to be distinct based on nuclear information. Alternatively, another possibility is that some misidentifications may be at the basis of the sequences deposited in GenBank.…”

Multilocus molecular systematics of the circumtropical reef-fish genus Abudefduf (Pomacentridae): history, geography and ecology of speciation

“…Recently, genetic variation of mitochondrial and two nuclear loci was examined across much of the geographic range of A. sexfasciatus and A. vaigiensis by Bertrand, Borsa & Chen (2017) . That study identified four highly distinct A. vaigiensis lineages , which did not form a monophyletic group relative to other closely related species those authors examined.…”

“…Although the genus has been subject to much recent phylogenetic study, those analyses used few genetic loci and did not include all known species within the genus. As a consequence, uncertainty persists regarding interspecific relationships and how many species of Abudefduf exist ( Bertrand, Borsa & Chen, 2017 ; Cooper, Smith & Westneat, 2009 ; Cooper et al, 2014 ; Wibowo, Toda & Motomura, 2017 ).…”

Johnston Atoll: Reef Fish Hybrid Zone between Hawaii and the Equatorial Pacific

“…Our example from Johnston Atoll is part of this biogeographic phenomenon of A. vaigiensis dispersal from the equatorial Pacific to the Hawaiian Islands. A. vaigiensis is a vigorous species which also recently invaded the Mediterranean Sea [39] and will hybridize with congeners elsewhere [40].…”